text: All bonds are depicted as horizontal or vertical lines. The carbon chain is depicted vertically, with carbon atoms sometimes not shown and represented by the center of crossing lines (see figure below). The orientation of the carbon chain is so that the first carbon (C1) is at the top. In an aldose, C1 is the carbon of the aldehyde group; in a ketose, C1 is the carbon closest to the ketone group, which is typically found at C2.
  The proper way to view a Fischer projection is to vertically orient the molecule in relation to the carbon chain, have all horizontal bonds point toward the viewer, and orient all vertical bonds to point away from the viewer. Molecules with a simple tetrahedral geometry can be easily rotated in space so that this condition is met (see figures). Fischer projections are commonly constructed beginning with a sawhorse representation. To do so, all attachments to main chain carbons must be rotated such that resulting Newman projections show an eclipsed configuration. The carbon chain is then positioned vertically upward with all horizontal attachments pointing toward the viewer. Finally, attachments to main chain carbons that face away from the viewer are placed in the vertical position of the Fischer projection, and those that face toward the viewer are placed in the horizontal position of the Fischer projection. Each intersection between a horizontal and vertical line on the Fischer projection represents a carbon in the main carbon chain.
  Fischer projections are effective representations of 3D molecular configuration in certain cases. For example, a monosaccharide with three carbon atoms (triose), such as the D-Glyceraldehyde depicted above, has a tetrahedral geometry, with C2 at its center, and can be rotated in space so that the carbon chain is vertical with C1 at the top, and the horizontal bonds connecting C2 with the Hydrogen and the Hydroxide are both slanted toward the viewer.
  However, when creating a Fischer projection for a monosaccharide with more than three carbons, there is no way to orient the molecule in space so that all horizontal bonds will be slanted toward the viewer. After rotating the molecule so that both the horizontal bonds with C2 are slanted toward the viewer, the horizontal bonds with C3 will be typically slanted away. So, after drawing the bonds with C2, before drawing the bonds with C3 the molecule must be rotated in space by 180° about its vertical axis. Further similar rotations may be needed to complete the drawing.
  This implies that in most cases a Fischer projection is not an accurate representation of the actual 3D configuration of a molecule. It can be regarded as a projection of a modified version of the molecule, ideally twisted at multiple levels along its backbone. For instance, an open-chain molecule of D-glucose rotated so that the horizontal bonds with C2 are slanted toward the viewer, would have the bonds with C3 and C5 slanted away from the viewer, and hence its accurate projection would not coincide with a Fischer projection. For a more accurate representation of an open-chain molecule, a Natta projection may be used.
  According to IUPAC rules, all hydrogen atoms should preferably be drawn explicitly; in particular, the hydrogen atoms of the end group of carbohydrates should be present.
   In this regard Fischer projection is different from skeletal formulae.